Are Leeks toxic to cats?

Leeks cause oxidative damage to red blood cells, leading to hemolysis (rupture) and subsequent anemia, while also causing gastrointestinal irritation.

There is no specific antidote for Allium poisoning. If your cat ate the leeks recently, the vet may make it vomit with an injected medicine: the 2005 toxicology brief says this can help a cat with no signs yet, if there are no complicating factors and it ate within the last one or two hours. Activated charcoal may follow, although the Merck Veterinary Manual says it is unknown whether it binds the sulfur compounds from Allium plants. Blood tests confirm the diagnosis by finding Heinz bodies (clumps of damaged hemoglobin inside red blood cells) and anemia, and the vet rechecks the blood over several days, when the anemia is usually at its worst. A cat with life-threatening anemia may need oxygen and a blood transfusion, and a drip (IV fluids) helps protect the kidneys. The 2005 toxicology brief says antioxidants such as sodium ascorbate (a form of vitamin C), vitamin E and N-acetylcysteine had little visible protective effect in cats poisoned by onion powder, and recommends a diet low in oxidants, avoiding semi-moist foods that contain propylene glycol.

No recovery times or survival figures for leeks were found. The 2005 toxicology brief says the outlook depends on the plant involved, how severe the anemia is and whether supportive care is started, and the Merck Veterinary Manual lists collapse and death among the possible outcomes of Allium poisoning. A 2016 review reports 4 cats poisoned by Allium plants that were recorded by the Veterinary Poisons Information Service between 1994 and 2008. Their signs included stomach and gut upset, lethargy, increased thirst, anemia and jaundice, and one cat died from bleeding into the chest and belly.

• Vegetable gardens. The leek is a hardy, cool-season vegetable, and Utah State University Extension says that in most areas it can be kept in the garden over winter, with soil heaped around the plants and a thick layer of mulch, leaves or soil on top.
• Kitchens. Leeks go into soups, salads and casseroles, and can be frozen, pickled, canned or dried at home. Cooking doesn't make them safe: a 2005 toxicology brief in Veterinary Medicine says cooking or spoilage does not reduce the potential toxicity of Allium plants, and a 2016 review says cooking, drying and processing don't remove it.
• Leftovers and ready-made foods. The 2005 toxicology brief lists juice, powdered cooking preparations, dried plant material and any food made from or containing an Allium plant as potentially toxic to dogs and cats. The Merck Veterinary Manual says poisoning in dogs and cats is most often linked to concentrated forms, such as dried flakes, powders and dry onion soup mixes.
• The Allium family. Leeks belong to the same group of plants (the genus Allium) as onions, garlic, chives, shallots and scallions, and the 2005 toxicology brief says all Allium species and the products made from them can be toxic to dogs and cats. Pet Poison Helpline says leeks, onion, garlic and chives are all poisonous to dogs, cats and livestock. The ASPCA lists the leek (Allium ampeloprasum) as toxic to dogs, cats and horses.
• The toxins are sulfur compounds. The Merck Veterinary Manual says chopping, cooking and chewing release them from the plant, and so does the action of bacteria in the gut. The ASPCA names n-propyl disulfide as the toxic principle in leeks.

• Don't share leeks, raw or cooked, or dishes made with them, such as soups and casseroles, with your dog or cat. The 2005 toxicology brief says cooking doesn't reduce the potential toxicity of Allium plants.
• Don't give leftovers that contain leeks, onion or garlic as a regular treat. The 2005 toxicology brief says poisoning can follow repeated small amounts as well as a single large one.
• Check the label before you share any food made for people, such as broth, a soup mix or baby food. The 2005 toxicology brief lists powdered cooking preparations and dried plant material among the potentially toxic forms, and the authors of a 1998 study advise against feeding cats baby food that contains onion powder.
• Put leek trimmings straight into a bin your pet can't open, and keep your dog out of the vegetable patch. Leeks can stay in the garden all winter.
• Keep onions, garlic, chives and shallots out of reach too. The 2005 toxicology brief says all Allium species can be toxic to dogs and cats, and Pet Poison Helpline says onion, garlic, chives and leeks are all poisonous to them.